This invention relates to methods for cleaning residues from the internal surfaces of chemical vapor deposition (CVD) chambers. The methods described are especially useful in integrated circuit manufacturing. Methods of the invention focus on determining the endpoint of cleaning a CVD chamber, especially when cleaning residues from the internal surfaces of the chamber following the deposition of ultra low dielectric constant films deposited using a silicon-based dielectric precursor and an organic-based porogen. The methods involve cleaning the chamber with a plasma while monitoring the intensity of one or more of the optical emission lines corresponding to removal of organic-based residue.
The use of low dielectric constant (low-k) materials is widespread in the integrated circuit manufacturing industry. Low-k films are commonly used as inter-metal and/or interlayer dielectrics because these films reduce delay in signal propagation due to capacitive effects. The lower the dielectric constant of the dielectric film, the lower the capacitance of the dielectric film and the lower the RC delay of the integrated circuit.
Low k dielectrics are conventionally defined as those materials that have a dielectric constant lower than that of silicon dioxide, that is k<4. However, with ever increasing technology demands, present efforts are focused on developing low-k dielectric materials with k less than 2.5, commonly referred to as ultra low-k (ULK) materials. One method of obtaining ULK materials involves forming porous carbon-doped oxide (CDO) films. These methods typically involve forming a composite film (referred to herein as a “precursor film”) containing two components: a porogen (typically an organic material) and a structure former or dielectric material (e.g., a silicon oxide containing material). Once the precursor film is formed on the substrate, the porogen component is removed, leaving a structurally intact porous dielectric matrix on the substrate. The introduction of air voids, combined with the carbon doping of the silicon oxide network, substantially lowers the overall dielectric constant of the film to produce the ULK film.
Common techniques for forming the precursor film include chemical vapor deposition (CVD) methods, including plasma enhanced CVD (PECVD) methods, wherein porogen precursor and structure former precursor compounds are co-deposited on a substrate. During this deposition process, residues will tend to adhere to the internal walls and surfaces of the reaction chamber. These residues, generally composed of silicon-based species and organic-based species, can build up on the inside of the chamber and can dissolve, detach or otherwise disperse through the chamber during subsequent processing, resulting in substrate contamination and yield loss. Consequently the residues that accumulate on the interior surfaces of the CVD chamber must be periodically removed. This accumulated deposition residue is typically removed from the interior surfaces of the CVD chamber using two types of cleaning procedures, plasma cleaning procedures and wet cleaning procedures.
Plasma cleaning procedures can be done using either in situ chamber cleans or remote chamber cleans. In in situ chamber cleans, the chamber clean chemicals are introduced into the CVD chamber in a gaseous state and plasma excitation within the CVD chamber is used to dissociate the chamber clean chemicals into reactive radicals and ions. In remote cleans, an independent plasma source is used to dissociate the gaseous chamber clean chemicals into reactive radicals and ions outside the CVD chamber, and the dissociated chamber clean chemicals are then introduced into the CVD chamber. In both in situ and remote chamber cleans, the reactive species in the CVD chamber react with the accumulated deposition residue to form gaseous products that are evacuated from the chamber.
After a number of plasma cleaning cycles, the performance of the CVD process degrades and a wet clean is required. In wet cleaning procedures the CVD chamber is vented to atmosphere and the interior surfaces of the reactor are physically scrubbed using appropriate cleaning solutions and/or abrasives. This type of cleaning procedure is time consuming, labor intensive, and requires reconditioning of the chamber once completed. Consequently improvements in the plasma cleaning procedure that extends the intervals between required wet cleans are critical to maintaining the highest possible CVD chamber throughput. Improvements in the plasma cleaning procedure can also result in a decrease in the degradation of the interior reactor surfaces and consequently, extended hardware lifetimes.
Oxidative in situ plasma methods have commonly been used for cleaning CVD chambers. These methods involve introducing an oxidizing agent such a fluorine-containing gas into the chamber and implementing a plasma to create strongly reactive ions and radicals. These strong reactive agents breakdown the residues that have built up on the internal surfaces of a chamber to form volatile species that are pumped away by vacuum. During the plasma cleaning process, it is important to determine when all of the residues have been removed. If the plasma process is not applied for a long enough period of time, residues will persist within the chamber. The accumulation of unremoved deposition residue can result in particle contamination issues and more frequent wet cleans. If the plasma process is applied for a longer period of time than necessary, overcleaning of the CVD chamber will result. Overcleaning the CVD chamber will result in premature degradation of the interior CVD chamber surfaces, particle contamination issues resulting from overexposure of the interior chamber surfaces to the cleaning plasma, and more frequent wet cleans. In addition to impacting wafer throughput, overcleaning the CVD chamber will also waste costly chemicals. Consequently one of the most critical steps in improving the plasma cleaning procedure is identifying a method that allows the endpoint of the plasma cleaning process to be correctly determined.
Some currently available techniques to determine the endpoint of a plasma cleaning process are described in U.S. Pat. Nos. 6,534,007 and 5,846,373. One method involves monitoring the ratio of the intensity of emission lines of a fluorine radical and a background gas (e.g., argon or nitrogen) during the plasma cleaning process. The other method involves monitoring the emission intensity of NO. These methods, however, while they may be effective for determining the endpoint of removing silicon-based residues, are completely ineffective for determining the endpoint of cleaning of both the silicon-based and the organic-based residues that result from the deposition of ULK precursor films. In particular, it has been found that using techniques appropriate for determining the endpoint for removing silicon-based resides, when applied to determining the endpoint for cleaning chambers after a ULK precursor deposition process, results in significant undercleaning of the CVD chamber and the accumulation of unremoved deposition residue inside the chamber.
What is needed therefore are improved methods for determining the endpoint for cleaning CVD chambers after a ULK precursor film deposition process.